Practice-based evidence arises from programs implemented in real-world settings. Program success may be judged on the basis of experience; however, formal evaluation studies of methodological rigor can provide a high level of credible evidence to inform public health practice. Such studies can be lengthy and expensive. Furthermore, even well-designed studies may not reach conclusive findings, for example, when a program lacks full implementation, when data systems do not have capacity to collect evaluation data, or when program implementation has not attained stability. An evaluability assessment is used to determine the capacity and readiness of a program for full-scale effectiveness evaluation. Evaluators at the Centers for Disease Control and Prevention use evaluability assessment as a preevaluation consisting of brief, focused, criteria-based assessments, document review, and a site visit. Evaluability assessment is used to guide investments in subsequent rigorously designed evaluations that yield conclusive findings to build strong and credible practice-based evidence.